//Array.prototype.forEach.call([1,2,3],function(item){console.log(item)})
let list = document.getElementsByTagName("li")
//方法1
//Array.prototype.forEach.call(list, function (item) { console.log(item) })
//方法2
HTMLCollection.prototype.forEach = Array.prototype.forEach
list.forEach(function (item) { 
  console.log(item)
})